Two years ago, under those same circumstances, the pressure and stress built up. Then, after a foot-fault call nobody will soon forget, it culminated in an ugly ending in her match against Kim Clijsters — Williams shaking her racket and threatening the official who made the call, then losing when she was given a point penalty on match point.

Williams missed last year’s U.S. Open with an injury.

And now, back in the 2011 semifinal, she will face top-ranked Caroline Wozniacki in the evening’s featured match.

The other semifinal pits No. 9 Samantha Stosur against 92nd-ranked Angelique Kerber of Germany. Stosur is trying for her second Grand Slam final. Kerber is trying to join Clijsters and Venus Williams as the third unseeded player to make a U.S. Open final.

Early last week, when Williams won her first singles match on Ashe since the ugly ending to the Clijsters semifinal, she insisted that night wasn’t going through her mind when she stepped on the court. Pressed on that, asked how she could simply set aside the ugliest moment in her brilliant career, she refused to budge.

“If anything, I thought, ’Wow, I’m back. I haven’t played in a long time,’” she said. “I’m telling you, out of sight, out of mind for me. You guys should try it.”

Despite being seeded 28th, Williams has looked like the best player in the tournament, almost from the beginning. She plays a power game, hits serves above 110 mph and intimidates simply by walking onto the court. She has yet to lose a set, same as in 2009 on her trip to the semifinals.

“I really try not to look so much across the net,” Ana Ivanovic said, when asked how she deals with Williams’ presence. Ivanovic lost 6-3, 6-4 in the fourth round.

The match against Wozniacki will be a contrast in styles. So far in the tournament, Williams has hit 128 winners against 81 unforced errors with 41 aces. Wozniacki’s stats: 73 winners, 98 unforced errors and nine aces.

Wozniacki has moved her way to No. 1 in the rankings by winning lots of matches at regular stops on the tour, but she does not have a Grand Slam title to her name.

She is a counterpuncher and wins by making her opponent hit one more shot, then another. Wozniacki is 0-2 lifetime against Williams, but they haven’t met since 2009. This will be their first match since Wozniacki got to No. 1 about a year ago, and it will be viewed by some as a referendum on Wozniacki’s worthiness as the world No. 1.

She’s not buying into that, though.

“To be honest, I don’t care,” she said. “I don’t care what people think and say or do. I care about what I know best. I go out there, and what I care about is that I give 100 percent every time.”

That’s never been in doubt. Whether she can counterpunch her way to a victory over Williams, however, is the big question.

“I definitely never give up. I always fight to the last point,” Wozniacki said. “I believe the match is never over until the last ball has been played.”

The other semifinal is a meeting between Kerber, a 23-year-old left-hander who would rise into the top 25 with a win, and Stosur, an Aussie who is turning the marathon match into an art form.

Stosur set the U.S. Open record with a 3 hour, 16 minute win over Nadia Petrova in the third round. Her next match featured a 17-15 tiebreaker against Maria Kirilenko, the longest in the history of the Grand Slams. Last year, she went 2 hours, 38 minutes against Elena Dementieva in a match that ended at 1:35 a.m.

She would, of course, take as long as needed to win a Grand Slam.

But, she conceded after her straight-sets victory over No. 2 Vera Zvonareva in the quarterfinals, “it’s always nice to finish them off in less than three hours.”

The match will be played far outside of the spotlight — on the Grandstand court starting at 6 p.m. and won’t be part of the coverage on CBS. The U.S. Tennis Association released a statement saying it gave the match second billing for a number of reasons.

“These factors included programming for U.S. Open ticket holders, competitive fairness for players, and the existing television windows for the tournament,” the statement said.